1. Field of the Invention
The present invention relates to a method for forming a flattened interlayer insulating film to cover the wiring layer or the like of a semiconductor integrated circuit device, and a method for manufacturing a semiconductor device.
2. Description of the Prior Art
In recent years, within the field of semiconductor integrated circuit devices (hereinafter, referred to as a semiconductor IC device), progress has been made toward achieving a much higher density, and an increasing number of such devices have multilayer wiring, i.e., wiring extended over several layers. In such a case, because of the frequent use of, especially, an aluminum material for the wiring, a need has developed for a method for forming a flattened interlayer insulating film at a low temperature of 500xc2x0 C. or lower.
Conventionally, flattening methods include: that shown in FIG. 1, which performs flattening by forming a film by a thermal chemical vapor deposition method (hereinafter, referred to as a TH-CVD method); a plasma enhanced chemical vapor deposition method (hereinafter, referred to as a PE-CVD method) or the like, heating the formed film, and then fluidizing the film; the etch back method shown in FIG. 2; and the chemical mechanical polishing method (hereinafter, referred to as a CMP method) shown in FIG. 3, which removes unevenness on the surface of the insulating film by etching or polishing.
In the case of the former method, as shown in FIG. 1A, a boro-phospho silicate glass film (hereinafter, referred to as a BPSG film) 4 is formed by a TH-CVD method, which uses any one of the following deposition gases:
(1) SiH4+PH3+B2H6+O2 (PH3: phosphine)
(2) TEOS+TMOP+TMB or TEB+O2 or O3 (TEOS: tetraethylorthosilicate (Si-(OC2H5)4), TMOP: trimethylphosphate (PO(OCH3)3)).
Alternatively, as shown in FIG. 1A, a BPSG film 4 is formed by a PE-CVD method, which uses any one of the following deposition gases:
(1) SiH4+PH3+B2H6+O2 
(2) TEOS+TMOP+TMB or TEB+O2.
For reference, see: J. Electrochem. Soc., 134.3,: 657, 1987, by Williams, D. S. and Dein, E. A; J. Vac.Sci. Technol., B1, 1:54, 1983, by Levin, R. M. and Evans-Lutterodt, K; Extended Abstract of Electrochem. Soc. Spring Meeting: 31, 1971, by Sato, J. and Maeda, K.
Then, as shown in FIG. 1B, the formed BPSG film 4 is heated to a temperature of about 850xc2x0 C., and thereby fluidized and flattened. In the case of a phospho-silicate glass film (hereinafter, referred to as a PSG film), a film is formed by a TH-CVD method, a PE-CVD method or the like, which uses the foregoing deposition gas minus the boron containing gas (B2H6, TMB or TEB), which film is then heated to a temperature of 1000xc2x0 C. or lower, and thereby fluidized and flattened.
In the case of the latter method, as shown in FIG. 2A and FIG. 3A, firstly, a non-doped silicate glass (hereinafter, referred to as a NSG film) 5 is formed by a TH-CVD method, a PE-CVD method or the like, which uses one of the following deposition gases, and then flattened:
(1) SiH4+O2 (TH-CVD method or PE-CVD method)
(2) TEOS+O2 or O3 (TH-CVD method)
(3) TEOS+O2 (PE-CVD method)
In the etch back method, as shown in FIG. 2B, a resist film 6 is formed on the NSG film 5 by a coating method, and then, as shown in FIG. 2C, the film 6 is subjected to etching to form a flattened NSG film 5a. In the CMP method, as shown in FIG. 3B, the NSG film 5 is formed, and then polished to flatten the surface and form a flattened NSG film 5b. 
In FIGS. 1 to 3, reference numeral 1 denotes a semiconductor substrate; 2 a base insulating film; and 3a and 3b wiring layers formed on the base insulating film 2.
Incidentally, the above-described flattening methods based on the etch back method or the CMP method are effective, especially when a low temperature is required, because these methods can be executed without heating, unlike the case of flattening by heating to fluidize. However, as shown in FIGS. 2A-2C, 3A and 3B, if any voids or recesses are formed between the wires 3a in the insulating film 5, the voids and recesses are left unchanged even after flattening. Currently available methods for forming insulating films having good gap-filling capabilities include a high-density PE-CVD method, a PE-CVD method, an atmospheric pressure TH-CVD method, an spin-on-glass (hereinafter, referred to as SOG) coating method, and the like. However, since these flattening methods do not use thermal fluidity, particularly when a high densification is attained by narrowing the spaces between the wiring, recesses cannot be completely filled.
On the other hand, in the flattening method based on fluidizing by heating, since thermal fluidity is utilized, as shown in FIG. 1, complete filling can be expected. At present, the BPSG film 4 is frequently used for such a purpose. However, heating to at least a temperature of 850xc2x0 C. must be carried out for fluidization. Thus, such a film cannot be applied to the base film 2 of the wiring 3a and 3b or the interlayer insulating film 4, where a low temperature is needed for formation. In particular, the film cannot be applied to an insulating film to cover the aluminum wiring layer. In this case, the temperature of fluidization can be somewhat lowered by increasing the concentration of boron or phosphorus. Even so, the temperature is not sufficiently low. Rather, new problems may occur, such as a reduction in the stability or humidity resistance of the insulating films 2 and 4. Similar problems may occur in the case of a PSG film, because a temperature of fluidization substantially equal to that for the BPSG film is necessary.
As an insulating film having a low fluidization temperature, a GeBPSG film formed by adding GeO2 to the BPSG film has been developed. However, the temperature cannot be lowered below about 750xc2x0 C. Thus, it is difficult to apply this film to a base film or an interlayer insulating film, for which a much lower temperature is required.
The fluidization temperature is preferably as low as possible, not only when aluminum, copper or the like is used for wiring in a semiconductor large scale integrated circuit (hereinafter, referred to as LSI) or the like, but also to prevent re-distribution of impurities from an impurity introduction region which is generally caused by heat.
An object of the present invention is to provide a method for forming an insulating film, capable of greatly reducing the fluidization temperature for flattening a surface, and a manufacturing method for a semiconductor device.
The inventors focused on the following points:
(1) the BPSG film or the phospho-silicate glass film (hereinafter, referred to as PSG film) is conventionally formed from a mixture of SiO2+P2O5+B2O3, or of SiO2+P2O5 (the PH3 of the deposition gas SiH4+PH3+B2H6+O2 is III valance phosphorus, and bonds with externally supplied oxygen to generate, not P2O3, but P2O5. This may be attributed to the fact that since PH3 itself contains no oxygen, when it is bonded with externally supplied oxygen, stable P2O5 is easily generated.);
(2) in the BPSG film of P2O5xe2x80x94SiO2, a eutectic point for the composition of 20 to 80% of P2O5 is theoretically 850xc2x0 C., and its fluidization temperature is dependent on the melting point of the P2O5 itself; and
(3) P2O3 has a melting point much lower than that of P2O5 as shown in Table 1.
Accordingly, the inventors theorized that the fluidization temperature would be lowered if the BPSG film or the PSG film contains mainly P2O3, instead of P2O5.
Accordingly, the present invention oxidizes a phosphorus containing compound in an oxygen deficient atmosphere to form a BPSG or PSG film having a high concentration of P2O3. The method may use, as a deposition gas, (1) a silicon and phosphorus-containing compound, wherein the phosphorus atom (P atom) is in the III valance form; or (2) a silicon containing compound or a silicon and phosphorus-containing compound containing oxygen, without addition of any oxygen or ozone.
The silicon and phosphorus-containing compound, containing a III valance P atom, may be selected from silicon and phosphorus-containing compounds having the following structural formulas:
A PSG film or the like was formed by using deposition gas containing the silicon and phosphorus-containing compound, and by a TH-CVD method or a PE-CVD method, and the composition of the formed film was determined by X-ray fluorescence analysis (XRF) or Fourier transform infrared spectroscopy (FTIR). The presence of high-concentration P2O3 in the formed film was verified. Then, a fluidization temperature of 700xc2x0 C. or lower was obtained. Further, it was found that it is possible to adjust a fluidization temperature by controlling a concentration of P2O3.
The inventors also found that it is possible to easily adjust concentration of P2O3 by controlling the deposition temperature and the gas flow rate of the silicon and phosphorus-containing compound (flow rate of inert gas carrier), or by controlling the concentration of oxidizing gas when an oxidizing gas is added.
If nitrogen (N2) is used as carrier gas for the silicon and phosphorus-containing compound, since N2 is a diatomic molecule, when a film is formed by reaction of plasma enhanced vapor deposition, it is assumed that the N2 dissociates and bonds with hydrogen in the film to form ammonia (NH3) in the film. Accordingly, the present invention uses an inert gas, e.g., argon or helium, as the carrier gas. Because of the low reactivity of argon or helium, the amount of ammonia in the film can be reduced to substantially zero.
Further, the use of inert gas, e.g., argon or helium, as the carrier gas, results in a great reduction in the concentration of phosphorus during heat treatment after deposition, enhancing controllability of the concentration of phosphorus.
In addition, by forming a film using only the silicon and phosphorus-containing compound, containing III valance phosphorus, the amount of carbon left in the formed film can. be greatly reduced. In this case, the adjustment of a phosphorus concentration can be made by controlling the ratio of flow rates of the silicon and phosphorus-containing compound and the foregoing inert gas in the deposition gas. Accordingly, in contrast to the prior art wherein a silicon containing compound containing no phosphorus is added in the deposition gas in order to adjust a phosphorus concentration, the present invention eliminates the silicon compound containing no phosphorus from the deposition gas. The silicon compound containing no phosphorus has Sixe2x80x94C bonds, causing carbon to be left during deposition. Thus, preferably, the addition of such a compound should be as little as possible, but can be added as occasion demands.
Furthermore, the film that has been formed as described above is subjected to nitrogen annealing and oxygen annealing, and then heated in an atmosphere containing moisture. This process is called steam annealing. Since the steam annealing has an oxidizing force stronger than that of normal oxygen annealing, residual III valance phosphorus is oxidized, and the moisture absorption resistance of the formed film is enhanced, thus improving film quality.
The foregoing can be established similarly for the BPSG film.